Many photodetectors, such as the photodiode and the conductor-insulator-semiconductor (CIS), provide output signal currents in response to electromagnetic radiation impinging thereon, on the order of nanoamperes (10.sup.-9 amperes). This order of photodetector currents assumes typical light intensities encountered in scene images and acceptably sized radiation sensitive areas, which, in a monolithic integrated circuit, are on the order of 10.0 mil.sup.2. Generally, there is a desire for such photodetector output currents to be converted to a voltage for operating subsequent photodetector signal processing circuitry. To effect such a conversion, one possibility would be to have the photodetector output current directed through a resistance. However, to obtain a sufficient voltage to operate subsequent signal processing circuitry, either a very large resistance or very sensitive subsequent circuitry is required, or both, because of the very small photocurrents generated by the photodetector.
Neither of these requirements--a high resistance or very sensitive subsequent circuitry--is readily met in a monolithic integrated circuit chip fabricated by typical processes to yield metal-oxide-semiconductor field-effect transistor (MOSFET) devices in the integrated circuit chip. Large resistances take a substantial amount of area in the chip major surface which has a detrimental effect on the chip cost. Small signal amplifiers constructed from MOS field-effect transistors typically require signals in excess of 100 millivolts to be successfully operated on by such amplifiers. Thus, an alternative means for converting the small output signals provided by the typical and desired photodetector structures is desirable.